> For a lot of stuff though ATProto is built in a way that you shouldn't have to host your own; you can implement your own algorithmic feed that reads from the Bluesky Relay's firehose, or your own frontend that still gets data from the Bluesky AppView.
ATProto isn't "built this way".
Twitter was also built in a way where you could implement your own stuff - and then Twitter took that away.
With Mastodon, there is one large instance (controlled by the non-profit Mastodon gGmbH). If they tried closing themselves off, their users would be losing access to the majority of people in the network. Plus, while non-profits aren't perfect, they don't have VC investors to answer to.
Bluesky could decide to stop publishing the firehose or restrict its APIs - just as Twitter did. Given that they control 99.55% of the network, they can close it off without worrying about their users losing access to anything. And Bluesky is a for-profit company that has raised around $30M in VC.
What you talk about isn't a feature of ATProto. It's a feature of being centralized and having a company willing to let you use their servers for free (at least for now). This was the case with Twitter for a long time. You could read the Twitter firehose and build your own apps and frontends getting data from the Twitter APIs - just as you can do from Bluesky today.
But unless there's a reason why shutting off the firehose/APIs would be bad for Bluesky, they can do that at anytime. It might anger some users (as Reddit and Twitter both did), but they control the network and network effects are powerful. For most Bluesky users, they'd continue using it because they aren't there for some open protocol. They're on Bluesky because Twitter became a nazi bar. Until we see real decentralization with ATProto, it's just a centralized network like Twitter or Reddit which hasn't shut off its firehose and public API yet. Hopefully that won't happen, but it certainly could.